That makes a lot more sense in the context of the struggle against Morgoth. He became a star, as you note. And he is the hope of Elves and Men in that through him the Valar relented and reentered Middle-earth to dispose of Morgoth once and for all - the Enemy of the Elves and the Men who were Elf-friends and allies.

Even assuming that Tolkien went back in and inserted a reference to Aragorn in his early writings, it begs the question of why, since as you also note, Aragorn's mission in life is to resolve a situation that didn't yet exist in the Heroic Age of Turgon and Hurin.

Thanks... that makes more sense. I'd forgotten that Earendil brings the valar back to middle-earth to fight Morgoth - that would explain the 'hope' part.